Circulator-modulator frequency control system



April 13, 1965 H. SCHARFMAN ETAL 3,178,652

CIRCULATOR-MODULATOR FREQUENCY CONTROL SYSTEM Original Filed April 4.1960 MICROWAVE DISCRIMINATOF? U 2 Lu 3 G Ll] E INVENTORS HOWARDSCHARFMAN I BURTON H. SMITH LEONARD VV. GEIER A 7' TOHNE' Y tall.

United States Patent M 6 Claims. (Cl. 331-) This is a continuation ofour copending application, Serial No. 19,723, filed April 4, 1960, nowabandoned.

This invention relates to frequency control high frequency generatorsand more particularly to the stabilization of the frequency of magnetronoscillators by utilizing a cavity referenced circula-tor-modulator loop.

Frequency stabilization of high frequency generators for long term drifthas been accomplished by several techniques including multi-cavitycoupling, Pound stabilization, and other AFC loop-type systems feedingback on the oscillator. The stability of such techniques and systernsare generally dependent upon a number of interrelated factors and theyrequire complex, sensitive, and costly components such as crystalcontrol oscillators and complex feedback circuits difficult ofadjustment and construction. Such techniques and systems are generallysingle function arrangements for frequency control and in addition tothe above-noted disadvantages do not function to isolate the generatorfrom the load nor may they addition-ally function as a duplexer ifdesired. Further, AM .and/ or FM modulation is not easily obtained, ifat Generally only one or the other of the above-noted functions areavailable and inasmuch as stability is not achieved by the directapplication of control signals to the generator, high potentials arerequired. Still further, short time stability is generally notpractically obtainable.

On the other hand, ferrite circulators have been used to isolate thegenerator from the load and to function as duplexers, but so far as isknown by the inventors ferrite circulators have not been applied norsuccessfully utilized for frequency controlof the high frequencygenerator with which it is generally associated.

These and other disadvantages and deficiencies of the prior art areovercome by the present invention which contemplates the provision of aferrite rotation circulator serially connected in the output line of ahigh frequency generator wherein the circulat-or is provided with afeedback loop containing a microwave discriminator for supplying asignal to the solenoid of the rotation circula'tor in 3,178,652 PatentedApr. 13, 1965 high loop gain is used. Further, the generator issimultaneously and substantially isolated from the load, duplexing maybe provided if desired, modulation may be easily applied in the feedbackloop for AM or PM modulation, frequency stability is provided withoutadditional or complex control elements, and short time stability may beprovided by merely extending the loop gain characteristic to highfrequencies.

These and other objects and features of the invention, the nature of thepresent invention and its advantages, will appear more fully uponconsideration of the specific illustrative embodiment shown in theaccompanying drawing and of the following detailed description of thisembodiment.

FIG. 1 is a partly perspective and partly diagrammatic view of anon-reciprocal multi-branch network, in accordance with the presentinvention; and

such a manner as to pull the frequency of the generator in the properdirection when it varies from a reference frequency. This isaccomplished by providing means for the proper adjustment of the phaseof signals reflected back to the high frequency generator through therotation circulator and superimposing a control signal, obtained bysampling the output signal, on .the solenoid of the rotator that isproportional in magnitude and sense to frequency variation. The conceptof frequency pulling by means of a single or multicavity referencedrotation circulator is basic to the invention which, althoughparticularly useful with CW oscillators, is also applicable to CW, FMCW, pulse, and pulse-Doppler systems.

The invention will provide stable operation for what would otherwise bedeviations in frequency for large frequency swings of the order of thepulling figure of the sources used, and is limited only by the stabilityof the cavity systemand the attainable loop gain of the system. Thisresults in a system which is independent, at least to the first order,of crystal unbalance and amplifier drift and is also independent oftemperature variations when a FIG. 2 is a graphic representation of thevoltage vs. frequency curve of a microwave discriminator suitable foruse with the invention.

in more detail, FIG. 1 illustrates a nonreciprocal four branch microwavenetwork constructed in accordance with the present invention. Forconvenience hereinafter the network will be designated as a circulatornetwork. The circulator connecting the terminals a, b, c, and dcomprises a circular waveguide 12 which tapers smoothly and graduallyfrom its lefthand end into a rectangular waveguide 11 and which isjoined near said end by a second rectangular guide 14 in a shunt orH-plane junction. Guide 14 is terminated in a reflectionless andpowerabsorbing termination 10. The rectangular waveguides 1' 1 and 14-will accept and support only plane waves in which the component of theelectric vector, which determines the plane of polarization of the wave,is consistent with the dominant TE mode in rectangular waveguide.Likewise, the dimension of guide 12 is preferably chosen so that onlythe several polarizations of the dominant 'IE mode in it can bepropagated. By means of the smooth transition from the rectangularcross-section of guide 11 to the circular cross-section of guide 1 1 tothe circular cross-section of guide 12, the TE mode, that wave energyhaving a plane of polarization parallel to the narrow dimension oftherectangular cross-section of guide 111, may be coupled to and from theTB mode in circular guide 12 which has a similar or parallelpolarization. Any other polarization of wave energy in guide 12 will notpass through the polarization-selective terminal comprising guide 11.Guide 14 is physically oriented with respect to guides 11 and 12 so thatthe TB mode in guide 14 is coupled by way of the shunt plane junctionbetween the rectangular cross-section of guide 14 and the circularcross-section of guide 12 into the particular TE mode in circular guide12 which is polarized perpendicular to the TE mode introduced by guide11. Thus, guides 11 and 14 comprise a pair of polarization-selectiveconnecting terminals by which wave energy in two orthogonal TE modepolarizations may be coupled to and from one end of guide 12.:Furthermore, these guides comprise a pair of con-jugately relatedterminals or branches inasmuch as a wave launched in one will not appearin the other.

A highly conductive reflecting vane 15, which may be in the order ofone-half Wavelength in length, may be diametrically disposed in circularguide 12 opposite the junction aperture of guide 14 to assist inreflecting into guide 14 these waves having their plane of polarizationcoincident with the plane of vane 15.

At the other end of guide 12 is a similar pair of polarization-selectiveconjugate terminals comprising rectangular guides 13 and 16 coupled toorthogonally related waves in guide 12. which waves are polarized inplanes 45 degrees inclined to the planes of the corresponding waves,respectively, to which guides 11 and 14 are coupled. Thus, guide 12tapers into a rectangular guide 13 which supports a wave polarized in aplane inclined 45 degrees with respect to the polarization of the wavein guide 11. Guide 12 is joined in a shunt plane junction by a secondrectangular guide 16 which is perpendicular to both guides 12 and 13 andwhich will accept waves from guide 12 having a plane of polarizationinclined at 45 degrees to the polarization of those waves accepted byguide 14. A highly conductive reflecting vane 17 may be positioned withrespect to the aperture of guide 16 and bears the same relation theretoas vane bears to the aperture of guide 14. It is obvious to one skilledin the art that any of a number of other well-known coupling means maybe employed in lieu of one or more of the waveguides 11, 13, 14, and 16to couple to and from the proper polarizations of waves in guide 12.

Intel-posed and carried between the first pair of conjugate terminalscomprising guides 11 and 14 and the second pair of conjugate terminalscomprising guides 13 and 16 in the path of wave energy passingtherebetween in guide 12 is suitable means of the type which produces anantireciprocal rotation of .the plane of polarization of theseelectromagnetic waves. For example, a Farada effect element having suchproperties functions such that an incident wave impressed upon a firstside of the element emerges on the second side polarized at a differentangle from the original Wave and an incident wave impressed upon thesecond side emerges upon the first side with an additional rotation ofthe same angle. Thus, the polarization of a Wave passing through theelement first in one direction and then in the other undergoes twosuccessive space rotations or space phase shifts in the same sense,thereby doubling the rotation undergone in a single passage. Asillustrated by way of example in the drawing, this means comprises aFaraday-effect element 24 with accompanying conical transition members25 and 26 which may be of polystyrene and are provided to cut downreflections from the faces of element 24, mounted inside guide 12approximately midway between the conjugate pairs.

As a specific embodiment, element 24 may be a block of magneticmaterial, such as, for example, nickel-zinc ferrite having a thicknessof the order of magnitude of a wavelength. This material has been foundto operate satisfactorily as a directionally selective Faraday-effectrotator for polarized electromagnetic waves to an extent up to 90degrees or more when placed in the presence of a longitudinalmagnetizing field of strength which is readily produced in practice andin such thickness is capable of transmitting electromagnetic waves, forexample, in the centimeter range, with substantially negligibleattenuation. Suitable means for producing the necessary longitudinalmagnetic field surrounds element 24 which means may be, for the purposeof illustration, a solenoid 27 mounted upon the outside of guide 12 andsupplied by a source 28 of energizing current. It should be noted,however, that element 24 may be permanently magnetized or element 27 canbe a permanently magnetized structure. The angle of rotation ofpolarized electromagnetic waves in such magnetic material isapproximately directly proportional to the thickness of the materialtraversed by the waves and to the intensity of the magnetization towhich the material is subjected, whereby it is possible to adjust theamount of rotation by varying or properly choosing the thickness of thematerial comprising element 24 and the intensity of magnetizationsupplied by solenoid 27.

In the simplified view of the phenomenon involved, a plane-polarizedwave incident upon the magnetic material in the presence of the magneticfield produces two sets of secondary Waves in the material, each set ofsecondary Waves being circularly polarized. The two sets of secondarywaves are circularly polarized in opposite senses and they travelthrough the medium at unequal speeds.

Upon emergence from the material the secondary waves in combination setup a plane-polarized wave, which is in general polarized at a differentangle from the original wave. It should be noted that the Faradayrotation depends for its direction upon the direction of the magneticfield. Thus, if the direction of the magnetic field is reversed, thedirection of the Faraday rotation is also reversed in space whileretaining its original relationship to the direction of the field.

A high frequency generator 30, such as a magnetron, the Rieke diagram ofwhich is known is connected to terminal a. Removable shims 31 may beprovided between the reference surface of the magnetron used indetermining the Rieke diagram to secure the proper phase adjustment forwaves, hereinafter described in detail, reflected back to the magnetron.Alternately, and preferably, means for providing the desired phaseadjustment as described hereinafter in detail is provided at guide 16and comprises an adjustable shorting element 32 forming a terminationfor guide 16 which functions to vary the phase of waves received fromthe magnetron and reflected back toward the magnetron.

The output wave in guide 13 is sampled by a probe 33, which preferablyprojects only slightly into guide 13 so as to disturb transmissiontherein only slightly and functions to pick up a monitoring potentialfrom the wave in guide 13. The probe 33 may be connected as through acoaxial transmission line 34 to a conventional microwave discriminator35, the output of which may be connected to an amplifier 36 which insome cases may be desirable to increase the output of the discriminator35 to a more suitable value. The output of the amplifier 36 is connectedto the solenoid 27 whereby the aforementioned output is superimposed onthe current supplied by source 28. It is obvious to those skilled in theart that wellknown directional coupling means other than a probe asdescribed herein may be used and that if desired a separate solenoid maybe provided in conjunction with solenoid 27 to receive the output signalof the discriminator 35. Further, any suitable microwave discriminatormay be used having a voltage vs. frequency curve different from thatshown in FIG. 2 to provide a control signal having the desired magnitudeand sense variation for frequency variation from a fixed reference.However, in such a case, additional biasing potentials and the like willbe necessary to provide a reference potential indicative of thereference frequency.

The mode of operation of the invention is as follows. A verticallypolarized wave introduced at terminal a from a high frequency generator30 such as, for example, a magnetron which has a pulling characteristicand acts as a source of wave energy into guide 11, travels past theaperture of guide 14 and its associated vane 15 unaffected therebyinasmuch as the effective polarization of these components isperpendicular to the polarization of the wave, and past transitionmember 26, to element 24. The thickness of element 24 and the potentialfrom source 28 are adjusted, as pointed out thereinbefore, to give a 45degree rotation of the plane of polarization in the same direction asthe angle existing between the first pair of terminals comprising guides11 and 14 and the second pair of terminals comprising guides 13 and 16.Thus, as shown in FIG. 1, the polarization of the wave is rotated 45degrees in a clockwise direction, as indicated by the arrow on element24 in the drawing, thereby bringing the plane of polarization of thewave into the preferred direction for transmission unaffected past guide16 and into the preferred polarization of passage through guide 13 toterminal b and a suitable load connected thereto. Substantially freetransmission is therefore afforded from terminal a to terminal b.

For a specific adjustment of the length of guide 16 when the magnetronis oscillating at the desired frequency, when a wave having the samepolarity as the wave heretofore described as leaving terminal b by guide13 is applied from means acting as a source toguide 13 or is a wavereflected back through guide 13 as the case may be, it will betransmitted unaifected past the conjugate guide 16 to element 24. ThisWave will be rotated 45 degrees by element 24 bringing the wave into ahorizontal polarization at the aperture of guide 14 into which it willbe reflected by vane 15 for absorption in termination 10. However, it isimportant to note that if the amount of rotation varies from 45 degreesa portion of this signal will be coupled to guide 11. Similarily, a waveleaving guide 16 and having the same polarization as a wave enteringguide 16 will be launched in guide 12 in a polarization conjugate toguide 13 and will travel to element 24 where it receives a further 45degree rotation bringing its plane of polarization into the preferreddirection for transmission through guide 11 to terminal a and magnetron30 acting now as a utilizing means. The microwave discriminator 35,having a voltage vs. frequency curve such as for example, as shown inFIG. 2, is adjusted so that itszero (or reference) voltage conditioncorresponds to the desired magnetron output frequency. Obviously, forthe zero voltage condition no feedback signal will be supplied tosolenoid 27 and the operation of the system will remain unchanged.However, for the proper adjustment of the length of guide 16 asdetermined, forexample, by use of the Rieke diagram for the magnetron3t} and the selected parameters of the network, or by experimentation,the magnitude and phase of the signal propagated toward the magnetron3t} from guide 16 will be changed from that as received by guide 16 whenthe magnetron drifts offfrequency.

The nature of the phase shifting operation accomplished by guide 16 issuch that by reason of the signal superimposed on solenoid 27, whichvaries the amount of rotation affected, the polarization of thereflected wave is varied in the proper direction such that at least aportion thereof is received by guide 11 and varies the pullingcharacteristic of the magnetron in such a direction as to pull thefrequency of the magnetron back toward the desired frequency. As is wellknown, pulling results from load susceptance and is generally avoidedand considered to be undesirable. Briefly, by way of, explanation in aquantitative manner, a lagging wave incident on the magnetron, such as,for example, that reflected from a capacitive load, always addssusceptance to the resonant system and reduces the magnetronfrequencies. Similarly, a leading wave incident on the magnetron andreflected from an inductive load always adds negative susceptance to theresonant system and increases the magnetron frequencies. As may now bereadily evident the preferred embodiment of the present inventionresults in frequency pulling in the proper direction by reason of theprovision and adjustment of the proper phase of a wave reflected back tothe magnetron by guide 16 in combination with variation of the directionand amount of rotation from 45 degrees effected by-the circulator. Thisvariation from the normal or steady state rotation of 45 degreesiscontrolled by the outputsignal of the discriminator the variations ofwhich output signal are proportional. and. due to frequency deviationsof the magnetron and are related in sense to the proper phase adjustmentprovided, for example, by guide 16.

An alternative but less flexible arrangement comprises elimination ofthe function of guide 16 as a shorting stub to vary the phase of andreflect a wave back to the magnetron and variationof the phase ofsignals incident onthe magnetron by adjustment of the number of shims.31. In this case guide 16 may be eliminated altogether or it mayfunction as anoutput part to receive, for example, a wave coupled toguide 14 from a directional coupler adapted to permit signals to traveltoward guide 12 through guide" 14 and the absorption of signalstraveling from guide 12 through guide 14.. In this case. the reflectedsignal incident. on?v the 'mgnetron. is derived from reflected signalsdue to mismatch and the like between the circulator and the load, eitherinherent in the system or planned.

It may now be obvious that when the sense of rotation provided by thediscriminator for frequency variations of the magnetron is correlatedwith the proper phase adjustment for signals-incident onthe magnetron,as the magnetron tends to increase in frequency susceptance is added topull the frequency back toward the reference frequency to which thediscriminator is turned and when the magnetron tends to decrease infrequency susceptance is subtracted to again pull the frequency backtoward the reference frequency.

Having thus analyzed the structure and characteristics of the invention,it will be readily apparent to those skilled in the art that manymodifications may be made without deviating from the spirit and scope ofthe invention. For example, modulation of the magnetron output signalmay be easily provided by inserting means in conventional manner in thediscriminator feedback loop for amplitude or frequency moduation ormodulation may be provided by other well-known means. The circulator maybe used asa duplexer for CW systems, and in conjunction with a fastferrite switch in the receiver arm, it may be used for duplexing inpulsed systems as well. Of course, in anycase the magnetron is alwaysisolated from the load.

In all cases, it is to be understood that the abovedescribedarrangements are simply illustrative of a small number of many possiblespecific embodiments which can.

represent applications of the principles of the invention.

Numerous and varied other arrangements can readily be devised inaccordance with said principles by those skilled in the art withoutdeparting from the spirit and scope of the invention.

What is claimed is:

1. In a tfrequency stabilizing system the combination comprising:

a section of waveguide adapted to support electromagnetic wave energy ina plurality of linear polarizations;

a first polarization-selective connection at a first'location along saidwaveguide coupled to a given one of said polarizations at said firstlocation;

a source of linearly polarized .wave energy connected to said firstconnection;

a second polarization-selective connection at a second location alongsaid waveguide coupled to a polarization of linearly polarized waveenergy therein related by a first angle to the polarization of saidfirst connection;

coupling means for sampling a portion of wave energy in said secondconnect-ion;

ferromagnetic means carried by said waveguide be tween said first andsecond locations for rotating the plane of polarization of incidentelectromagnetic wave energy through a second angle substantially equalto said first angle;

frequency discriminator means connected between said coupling means andsaid ferromagnetic means for varying said second angle of rotationinaccordance withfrequency variations of energy in said coupling means;

and means connected to said waveguide disposed be- !tween said sourceand said second connection for selectably adjusting the phase of energypropagated toward. and incident on said source.

2. In a (frequency stabilizing system the combination comprisingzasection of waveguide adapted to support electromagnetic .wave energy ina plurality of linear polarizations;

a first polarization-selective connection at a first location along saidwaveguide coupled to-a given one of said polarizations at saidfirst'location;

a source of linearly polarized wave energy connected to said firstconnection;

a second polarization-selective connection at a second location alongsaid Waveguide coupled to a polarization of linearly polarized waveenergy therein related by a first angle to the polarization of saidfirst connection;

a load circuit connected to said second connection for receiving waveenergy and reflecting a portion of said received wave energy;

coupling means for sampling a portion of wave energy in said secondconnection;

ferromagnetic means carried by said waveguide between said first andsecond locations for rotating the plane of polarization of incidentelectromagnetic wave energy through a second angle substantially equalto said first angle;

frequency discriminator means connected between said coupling means andsaid ferromagnetic means for varying said second angle of rotation inaccordance with frequency variations of energy in said coupling means;

and means connected to said waveguide disposed between said source andsaid first connection for selectably adjusting the phase of energypropagated toward and reaching said source.

3. In a frequency stabilizing system the combination comprising:

a section of waveguide adapted to support electromagnetic wave energy ina plurality of linear polarizations;

a pair of polarization-selective connections at a first location alongsaid waveguide each coupled to an orthogonal polarization of linearlypolarized wave energy at said first location;

a source of linearly polarized wave energy connected to one of saidconnections;

a polarization-selective connection at a second location along saidwaveguide coupled to a polarization of linearly polarized wave energytherein related by a first angle to the polarization of said oneconnection at said first location;

coupling means for sampling a portion of wave energy in said connectionat said second location;

ferromagnetic means carried by said waveguide between said first andsecond locations for rotating the plane of polarization of incidentelectromagnetic wave energy through a second angle substantially equalto said first angle;

frequency discriminator means connected between said coupling means andsaid ferromagnetic means for varying said second angle of rotation inaccordance with frequency variations of energy in said coupling means;

and means connected to said waveguide disposed between said source andsaid connection at said second location for selectably adjusting thephase of energy propagated toward and reaching said source.

4. In a frequency stabilizing system the combination comprising:

a section of waveguide adapted to support electromagnetic Wave energy ina plurality of linear polarizations;

a first polarization-selective connection at a first locati-on alongsaid waveguide coupled to a given one of said polarizations in saidwaveguide;

a source of linearly polarized wave energy connected to said firstconnection;

second and third polarization-selective connections at a second locationalong said waveguide each coupled to an orthogonal polarization oflinearly polarized wave energy at said second location and related by afirst angle to the polarization of said first connection, said secondconnection being terminated by an adjustable short;

5. In a frequency stabilizing system the combination comprising:

a section of waveguide adapted to support electromagnetic Wave energy ina plurality of linear polarizations; first and secondpolarization-selective connections at a first location along saidwaveguide each coupled to an orthogonal polarization of linearlypolarized wave energy at said first location;

a source of linearly polarized Wave energy connected to said firstconnection;

means connected to said second connection for preventing energy receivedby said second connection from said Waveguide from returning there-to;

third and fourth polarization-selective connections at a second locationalong said Waveguide each coupled to an orthogonal polarization oflinearly polarized wave energy at said second location and related by afirst angle to the polarization of said first connection, said fourthconnection being terminated by an adjustable short;

coupling means for sampling a portion of wave energy in said thirdconnection;

ferromagnetic means carried by said Waveguide between said first andsecond locations for rotating the plane of polarization of incidentelectromagnetic wave energy through a second angle substantially equalto said first angle for coupling energy in said first connection to saidthird connection;

and frequency discriminator means connected between said coupling meansand said ferromagnetic means for varying said second angle of rotationin accordance with frequency variations of energy in said couplingmeans.

6. In a frequency stabilizing system the combination comprising:

a section of waveguide adapted to support electromagnetic wave energy ina plurality of linear polarizations;

first and second polarization-selective connections at a first locationalong said waveguide each coupled to an orthogonal polarization oflinearly polarized wave energy at said first location;

a source of linearly polarized wave energy connected to said firstconnect-ion;

means connected to said second connection for preventing energy receivedby said second connection from said waveguide from returning thereto;

third and fourth polarization-selective connections at a second locationalong said waveguide each coupled t-o anorthogonal polarization oflinearly polarized wave energy at said second location and related by afirst angle to the polarization of said first connection;

a load circuit connected to said third connection receiving wave energyand reflecting a portion of said received wave energy;

coupling means for sampling a portion of wave energy in said thirdconnection;

ferromagnetic means carried by said waveguide between said first andsecond locations for rotating the plane of polarization of incidentelectromagnetic wave energy through a second angle substantially equalto 9 said first angle for coupling energy in said first connection tosaid third connection;

frequency discriminator means connected between said coupling means andsaid ferromagnetic means for varying said second angle of rotation inaccordance with frequency variations of energy in said coupling means;

and means connected to said waveguide disposed between said source andsaid first connection for select- 10 ably adjusting the phase of energypropagated toward and reaching said source.

References ited by the Examiner UNITED STATES PATENTS JOHN KOMINSKI,Acting Primary Examiner.

1. IN A FREQUENCY STABILIZING SYSTEM THE COMBINATION COMPRISING: ASECTION OF WAVEGUIDE ADAPTED TO SUPPORT ELECTROMAGNETIC WAVE ENERGY IN APLURALITY OF LINEAR POLARIZATIONS; A FIRST POLARIZATION-SELECTIVECONNECTION AT A FIRST LOCATION ALONG SAID WAVEGUIDE COUPLED TO A GIVENONE OF SAID POLARIZATIONS AT SAID FIRST LOCATION; A SOURCE OF LINEARLYPOLARIZED WAVE ENERGY CONNECTED TO SAID FIRST CONNECTION; A SECONDPOLARIZATION-SELECTIVE CONNECTIUON AT A SECOND LOCATION ALONG SAIDWAVEGUIDE COUPLED TO A POLARIZATION OF LINEARLY POLARIZED WAVE ENERGYTHEREIN RELATED BY A FIRST ANGLE TO THE POLARIZATION OF SAID FIRSTCONNECTION; COUPLING MEANS FOR SAMPLING A PORTION OF WAVE ENERGY IN SAIDSECOND CONNECTION; FERROMAGNETIC MEANS CARRIED BY SAID WAVEGUIDE BETWEENSAID FIRST AND SECOND LOCATIONS FOR ROTATING THE PLANE OF POLARIZATIONOF INCIDENT ELECTROMAGNETIC WAVE ENERGY THROUGH A SECOND ANGLESUBSTANTIALLY EQUAL TO SAID FIRST ANGLE; FREQUENCY DISCRIMINATOR MEANSCONNECTED BETWEEN SAID COUPLING MEANS AND SAID FERROMAGNETIC MEANS FORVARYING SAID SECOND ANGLE OF ROTATION IN ACCORDANCE WITH FREQUENCYVARIATIONS OF ENERGY IN SAID COUPLING MEANS; AND MEANS CONNECTED TO SAIDWAVEGUIDE DISPOSED BETWEEN SAID SOURCE AND SAID SECOND CONNECTION FORSELECTIVELY ADJUSTING THE PHASE OF ENERGY PROPAGATED TOWARD AND INCIDENTON SAID SOURCE.